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of Alternative Technologies for Freshwater Augumentation
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1.2 Evaporation Reduction
|Water Evaporation Retardants
India, the use of Water Evaporation Retardants (WER) is being
investigated as a water conservation measure in surface waters. Control
of evaporative losses is being effected using Ceto-Stearyl alcohol, a
blend of saturated fatty alcohols, previously imported at high cost and
not readily available in India. India's first fatty alcohol plant was
commissioned in 1981 at Jalgaon, Maharashtra, by Aegis Chemical
Industries Ltd., using an exclusive technology based on an high pressure
hydrogenation technology developed in collaboration with Haldor Topsoe,
Denmark. The plant is one of the few in the world and the only one in
India, producing alcohols to international specifications.
1983, Aegis successfully developed an effective water evaporation
retardant, Acilol TA 1618 WER, an emulsion based on fatty alcohols
manufactured from natural vegetable oils. Acilol TA 1618 WER was
developed in the laboratory after extensive research aimed at
identifying a product compatible with the climatic conditions of the
country. Field trials were conducted in March 1984 with the help of
Gujarat Engineering Research Institute. These trials confirmed the
effectiveness of Acilol TA 1618 WER.
A dispensing technique
for applying Acilol TA 1618 WER to water surfaces, consisting of barrel
tanks with a drip feed arrangement mounted on "Floating Rafts"
anchored at different points on the lakes or reservoirs, was also
developed to suit Indian conditions. The first major project using this
technique to conserve water was undertaken by the Public Health
Engineering Department (PHED), Jaipur, at Ramgarh Lake in April, 1985.
About 50 mg/m2/d of the chemical is required and can result in a savings
of about 30% of the daily loss of water due to evaporation.
Evaporative losses can be controlled using various technologies. For
example, the use of mono molecular organic surface films has been shown to
be an efficient technology for reducing such losses. The mono molecular
film is applied to an open surface water storage area and allowed to over
the water surface. Typical mono molecular films are comprised of
long-chain fatty alcohols such as cetyl alcohol (hexadecanol) and stearyl
alcohol (octadecanol). These chemical not only suppress evaporation but
also prevent mosquito breeding in the water. The use of stearyl alcohol in
doses of up to 70 g/cm2 can reduce evaporative losses by up to 55% of the
loss due to evaporation from a free water surface. However, the economics
and extent of use of this technology are yet to be explored and
Extent of Use
Use of surface films to reduce evaporative losses is principally in arid
and semi-arid regions.
Operation and Maintenance
The operation and maintenance requirements of this technology are
negligible. Maintenance is required only for the rafts and boats, which
may be locally constructed, used during the application of the evaporation
retardants. No specialized skill is required.
Level of Involvement
The implementation of this technology is generally carried out by
government departments, primarily the public health engineering and water
supply departments. In India, it is now being promoted by various state
government agencies and local authorities. Generally, control of
evaporation is focused at the government level having prime responsibility
for water resources management.
No cost data were available as this technology remains largely
Effectiveness of the Technology
Of the various substances capable of forming mono molecular layers on a
water surface, fatty alcohols in their pure form have been found to be
most suitable and effective in retarding evaporation with no side effects
(AIT, 1982). Savings from the prevention of water loss due to evaporation
have been reported to be as high as 0.70 million cubic metres of water
(equivalent to one month's water supply for Jaipur City, India) using
Cetyl and Stearyl Alcohol as an evaporation retardant.
The technology is most suitable in small surface water storages where
there are no strong winds to disrupt the retardant layer.
Use of evaporation control techniques requires a small capital
investment. Locally constructed rafts can be used in its application, and
skilled labour is not required, except for operation of motorized boats.
Fatty alcohols present no hazards in handling, and are non-inflammable,
non-toxic, and non-irritating. There are no known harmful effects, making
this technology safe for application on drinking water lakes and
reservoirs. There are also no known ecological ramifications, as the
alcohols contain straight chain carbon compounds which are biodegradable
and permeable to oxygen.
The fatty alcohols used as WERs are not readily available and are
costly. Historically, fatty alcohols were produced only by sperm whales or
by sodium reduction of animal oils and fats. It was only after the
development of high pressure hydrogenation process that good quality fatty
alcohols are now commercially available. However, this is a very advanced
technology, and requires trained and skilled staff to operate.
There are no known problems with cultural acceptability.
Further Development of the Technology
More research is necessary in the area of stabilising the chemical film
in the face of high wind velocities. Properties such as rate of spreading,
specific resistance to evaporation and surface viscosity are required to
be measured in evaluating the efficiency of the retardant.
Asian Institute of Technology, Water Engineering and
Management Program, Post Office Box 2754, Bangkok, Thailand. Tel. 00 662
516 0110, Fax: 00 662 516 2126, E-mail: firstname.lastname@example.org.
A.C. Desai, T.K. Iyer, and V.M. Tople 1990. Use of Water Evaporation
Retardants for Water Conservation, Journal of Indian Water Works
Association, April-June, 193-194.
Asian Institute of Technology (AIT) 1982. Evaporation Control Using
Monomolecular Organic Surface Films. AIT Research Report No. 1982-2,
Division of Water Resources Engineering, AIT, Bangkok.